title: Dislodgment and accelerated degradation of Ras.
abstract: Membrane anchorage of Ras oncoproteins, required for transforming activity, depends on their carboxy-terminal farnesylcysteine. We previously showed that S-trans,trans-farnesylthiosalicylic acid (FTS), a synthetic farnesylcysteine mimetic, inhibits growth of ErbB2- and Ras-transformed cells, but not of v-Raf-transformed cells, suggesting that FTS interferes specifically with Ras functions. Here we demonstrate that FTS dislodges Ras from membranes of H-Ras-transformed (EJ) cells, facilitating its degradation and decreasing total cellular Ras. The dislodged Ras that was transiently present in the cytosol was degraded relatively rapidly, causing a decrease of up to 80% in total cellular Ras. The half-life of Ras was 10 +/- 4 h in FTS-treated EJ cells and 27 +/- 4 h in controls. The dislodgment of membrane Ras and decrease in total cellular Ras were dose-dependent: 50% of the effects occurred at 10-15 microM, comparable to concentrations (7-10 microM) required for 50% growth inhibition in EJ cells. Higher concentrations of FTS (25-50 microM) were required to dislodge Ras from Rat-1 cell membranes expressing normal Ras, suggesting some selectivity of FTS toward oncogenic Ras. Membrane localization of the prenylated G beta gamma of heterotrimeric G proteins was not affected by FTS in EJ cells. An FTS-related compound, N-acetyl-S-farnesyl-L-cysteine, which does not inhibit EJ cell growth, did not affect Ras. FTS did not inhibit growth of Rat-1 cells transformed by N-myristylated H-Ras and did not reduce the total amount of this Ras isoform. The results suggest that FTS affects docking of Ras in the cell membrane in a rather specific manner, rendering the protein susceptible to proteolytic degradation.
authors.affiliation: Department of Neurobiochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
authors.forename: R
authors.initials: R
authors.lastname: Haklai
authors.forename: M G
authors.initials: MG
authors.lastname: Weisz
authors.forename: G
authors.initials: G
authors.lastname: Elad
authors.forename: A
authors.initials: A
authors.lastname: Paz
authors.forename: D
authors.initials: D
authors.lastname: Marciano
authors.forename: Y
authors.initials: Y
authors.lastname: Egozi
authors.forename: G
authors.initials: G
authors.lastname: Ben-Baruch
authors.forename: Y
authors.initials: Y
authors.lastname: Kloog
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005204:Farnesol / Q000031:analogs & derivatives / Q000494:pharmacology; D006131:Growth Inhibitors / Q000494:pharmacology; D008745:Methylation / Q000187:drug effects; D027384:Oncogene Proteins v-raf; D051381:Rats; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000494:pharmacology; D015682:Retroviridae Proteins, Oncogenic / Q000494:pharmacology; D012459:Salicylates / Q000494:pharmacology; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000111:Acetylcysteine; D005204:Farnesol; D006131:Growth Inhibitors; D027384:Oncogene Proteins v-raf; D018719:Erb-b2 Receptor Tyrosine Kinases; D015682:Retroviridae Proteins, Oncogenic; D012459:Salicylates; D018631:ras Proteins; C093323:farnesylthiosalicylic acid; C068268:N-acetyl-S-farnesylcysteine